GROUP III. PTERIDOPHYTA : EQUISETIN.E. 



381 



mented into nodes and internodes. At each node is borne a whorl of scale- 

 leaves forming a continuous sheath. The branches, as also the adventi- 

 tious roots, spring from the nodes, a bud being developed in the axil of each 

 leaf, and an adventitious root from the base of each bud ; but in the 

 sub-aerial shoots the rudimentary roots do not grow out, whilst in the 

 subterranean shoots relatively few of the buds grow into branches. In 

 certain species (E. arvenie, silvaticum, maximum, palmfre, etc.) some of the 

 subterranean branches 

 become tuberous. 



The sub-aerial shoots 

 generally live for one 

 season only, and are her- 

 baceous in texture, but 

 in some species they 

 persist (e.g. E. hiemale, 

 trachyodon, variegatum). 

 They are generally green 

 in colour, and their sur- 

 face is more or less 

 strongly ribbed. Some 

 of these shoots are sterile, 

 whilst others are fertile, 

 bearing the sporangia. 

 In most species the 

 sterile and fertile shoots 

 are alike (Equiseta ho- 

 mophyadica), but in the 

 four species E. arvense, 

 maximum, silvaticum, 

 pratense (Equiseta hete- 

 rophyadica) they are 

 more or less widely dif- 

 ferent. Thus in E. 

 arvense and maximum, 

 the fertile shoots are 

 developed early in the 

 spring, and are un- 

 branched, whereas the 

 copiously branched 

 sterile shoots are not 

 developed till the sum- 

 mer ; moreover the fer- 

 tile shoots are not green. 

 In E. pratense the dif- 

 ference between the 



PIG. 227. Median longitudinal section of the apical por- 

 tion of a vegetative shoot of Equisetum arvense ; p apical 

 growing-point ; g bud-rudiment ; g'-g'" stages in the de- 

 velopment of lateral buds; v r> developing adventitious 

 roots on the buds ; TH central ground tissue ; vs develop- 

 ing (common) vascular bundle; n nodal diaphragms, 

 (x 26: after Strasburger ) 



fertile and sterile shoots is le.^s marked, the former bearing a few whorls 

 of simple branches. In E. silvaticum the fertile shoot has no branches at 

 first, but alter the [shedding of the spores the terminal cone dies off, the 



